When a metal rod `M` is dipped into an aqueous colourless concentrated solution of compound `N` the solution turns light blue.Addition of aqueous `NaC

Monjur Alahi

When a metal rod `M` is dipped into an aqueous colourless concentrated solution of compound `N` the solution turns light blue.Addition of aqueous `NaCl` to the blue solution gives a white precipitate `O`.Addition of aqueous `NH_(3)` dissolves `O` and gives an intense blue solution.
The metal rod `M` is :
A. `Fe`
B. `Cu`
C. `Ni`
D. `Co`


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Salim Ahmed Kawsar

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Correct Answer - B
`Cu(M)+AgNO_(3)(N)`(queous colourless solution) `to` Resultant solution contains `Cu(NO_(3))_(2)` (blue solution) and `AgNO_(3)` (colourless solution)
Note: Here it is considered that complete `AgNO_(3)` is not utilized in the reaction.
`AgNO_(3)(aq)+NaCl(aq) to AgCl darr`(white) `(O)+NaNO_(3)`
Solution containing white ppt. of `AgCl` also contains `Cu(NO_(3))_(2)` which developed deep blue colouration with aqueous `NH_(3)` solution
`AgCl darr ("white")+2NH_(3)(aq.) to [Ag(NH_(3))_(2)]^(+)`
`Cu(NO_(3))_(2)(aq.)+4NH_(3) (aq.) to [Cu(NH_(3))_(4)](NO_(3))_(2)` (deep blue solution)
So, Metal rod `M` is `Cu`.
The compound `N` is `AgNO_(3)` and the final solution contains `[Ag(NH_(3))_(2)]^(+)` and `[Cu(NH_(3))_(4)]^(2+)`

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